Understanding Herd Immunity
Written and Posted on Facebook By R. Dennis Garcia
Dear friends and policy-makers,
When May 1 comes and we go out of our homes, we will not be immune to COVID-19 any more than we were before March 16, except for the few of us who were infected in the preceding 6 weeks. Indeed, if 10,000 Filipinos would have been infected by May 1, this would only amount to 0.009% of the PH population, hardly a dent towards obtaining herd immunity against the dreaded virus.
At the onset of the lockdown on March 16, the doubling time of COVID-19 cases was 5 days. By April 15, as an effect of the lockdown, the doubling time had prolonged to 13.8 days.
The Phl population is 110M. To achieve a sizable herd immunity, we generally have to have at least 70% of the population to have been infected by COVID-19, and to have recovered.
Over how long a time can we achieve that 70%?
Once the lockdown is lifted on May 1, if there are 10,000 Filipinos infected by then, and if people behave as they did before March 16 (inadequate social distancing, unimpeded outside activities, no substantial use of masks in public), it will require roughly thirteen doubling times, if viral spread is transferred efficiently from person to person, in order to infect 82M Filipinos. With a 5-day doubling time, the date by which 82M Filipinos would have been infected will be as early as July 5. 82M is 74% of the Phl population, enough for herd immunity. As the viral transfer becomes inefficient when more people become infected and recover, if the doubling time is spaced out to 9 days, the new date by which 82M Filipinos will be infected will be August 26. Currently, on April 15, due to the lockdown’s inhibiting effect on the spread of the virus, the doubling time has prolonged to 14 days. If we assume that when the lockdown is lifted on May 1, and we can still have a 14-day doubling time (because people will be good at preventing horizontal transfer as they go back to work and school), we will achieve the 82M Filipinos infected by October 17 (ie., thirteen doubling times).
In all of the above scenarios, if the target herd population to be infected is 82M Filipinos, and based on Chinese data, 20% of infected people will become severely ill, this means that 16.4M Filipinos (of the 82M) will need in-patient hospital care between May 1 to October 17. So, the huge question is: will the hospitals throughout Metro Manila and the rest of the country be able to provide beds, HCWs, ventilators and medications to admit and treat 16.4M Filipinos between May 1 to October 17? If we divide the 16.4M over 5 & 1/2 months (to October 17), the number will be about 3M admissions/month. Where will we get these beds, medications, ventilators and personnel? Another problem is that when moderately ill COVID-19 patients are hospitalized, the length of stay lasts 2-3 weeks, tying up a hospital bed for a prolonged time. Yet another problem is that, as the hospital industry is unable to provide the necessary hospital care to those who need it, the mortality rate will rise compared to what it is now.
Prolonging the lockdown will continue to slow down the spread, perhaps past 2020. Otherwise, a quickly developed and approved vaccine is the only real solution for an illness with no clear effective treatment. The former is untenable much longer because people are growing hungry, using up their savings, losing their jobs, while government has finite resources by which to feed the people, and, heaven forbid, law and order may break down. The government will have to find the best balance at allowing a gradual lifting of the lockdown to allow essential industries to operate, allowing less-at-risk working populations to return to employment, while shielding the elderly and those with co-morbidities at home, and enforcing strict and punishable rules on containing the spread of infection by having masked civilians on the streets, offices and schools; encouragement of home-based work, and well thought-out mass transportation arrangements, among many things.
Otherwise, for the health care industry to not collapse in the 3-4 weeks after the lockdown is lifted on May 1, the following have to be present by then, or within 2 weeks of that date:
1. Testing capacity should be adequate for the whole Phl. Those who are sick have to be tested, so that every ill person is identified, treated, quarantined and/or hospitalized.
2. Quarantine facilities in every town, city and province should be ready for occupancy, numbering in the thousands of beds for big cities.
3. The LGU should be able to fund the needs of the quarantine facility.
4. Multiple COVID-contact tracking teams employed by each local government, whose job will be to do contact tracing of all COVID+ people and their contacts, should be in existence. Their job will be to see to it that the COVID+ patients and their contacts are staying at home, if they are clinically well and the home is big enough, or are housed in the LGU’s quarantine facility. Quarantining is the best way to protect the COVID+ patient’s family and housemates from becoming ill themselves, especially for people who live in one-room homes. Placing them in the quarantine facility will also prevent them from unnecessarily occupying a much needed hospital bed, which should be saved for the 20% of sick and elderly people who really need these beds. The hospitalized COVID+ cases can also be discharged to the quarantine facility, to finish the quarantine period, so that they do not infect their housemates if and when they go home too early.
5. The people who test positive, and those suspected to have it, should be placed in the quarantine facility, if not in their homes, for the obligatory number of days. This process will shield the community and limit the virus’ spread.
6. National and local governments have to designate the local hospital which will take in the COVID+ and probable cases all over the country, down to the smallest town. The medical, nursing and HCW staffs have to be increased, correspondingly, to the expected huge increase in workload.
7. The moderately and critically ill will be admitted to appropriately staffed and stacked government COVID-19-designated and private hospitals.
8. Appropriate numbers and volume of PPEs, pulse oximeters, oxygen tanks, ventilators, medications and other medical needs should be budgeted for and obtained.
9. The goverment needs to continue to support private hospitals, which will continue to provide for the bulk of in-patient care, as has been noted in Metro Manila.
10. Most importantly, the public has to be continuously reminded that going out of one’s home everyday is a life-and-death decision, and should be considered as such.
Unfortunately, this problem will not go away like a bad dream when we open our eyes in the morning. By having a populace well-educated and conscious of how to avoid getting the infection and spreading it to others, and with the necessary preparations of the government and private sectors through testing, pursuing ill people and their contacts, quarantining, protecting HCWs, and bracing hospitals, which are the last strongholds of the battle, we can see a situation wherein the Filipino population can attain a recovered number of people necessary to attain herd immunity over a manageable prolonged time period, like over 2-3 years (unless we are fortunate to have a vaccine within a year), while avoiding a total collapse of the hospital and health care industries in a situation of anarchy.
We do hope and pray for the best and God’s grace, but we all have to concretely realize what we are up against in the next many months.
R. Dennis Garcia
Infectious Disease Physician
IMPORTANT: This FB Post has been copied in verbatim without any editing or modification and with knowledge of author.