It is a matter of weighing benefits and risks and finding a right balance after doing due diligence
By Lim Poh Lian, Published The Straits Times, 28 Nov 2020
Would you take the Covid-19 vaccine, if it's available?
With the announcements of three Covid-19 vaccines achieving excellent rates of effectiveness, that is the question everyone is asking themselves.
The United States' Food & Drug Administration (FDA) will meet on Dec 10 to discuss the emergency use authorisation (EUA) of Pfizer's Covid-19 vaccine. If approved, Covid-19 vaccination for the highest risk groups could start in the US before Christmas.
Whether a vaccine should be used depends on several critical factors. Vaccine effectiveness is the obvious first step. However, it must be considered together with vaccine safety.
Vaccine safety is absolutely essential when considering vaccinating millions of people. So, what should we know about Covid-19 vaccine safety, and how should we think about it?
It is useful to first ask: "What is safety?" We could start with a dictionary definition: "The condition of being protected from danger, risk, or injury."
I suggest a pragmatic definition: Safety is finding an acceptable balance between risks and benefits, after doing due diligence.
This approach allows us to move forward, rather than getting stuck in analysis paralysis. After all, we make risk-benefit decisions every time we get in a car, board a plane, or cross the road. We manage the risks by putting in place systems to ensure road and air travel is as safe as possible.
We accept the risks when we get on an airplane, because the alternative would be a very long journey by road or sea, or not going anywhere at all.
We make similar risk-benefit judgments in medical practice. Vaccine safety is no different. Can we give an absolute guarantee that no one will ever experience any side effects or be harmed by a vaccine? Obviously not. Vaccines are medications, and all medications have risks and side effects, as well as situations when they should not be used.
The issue of side effects
So, what side effects should we look for when considering whether to use a vaccine?
There are two categories: danger and discomfort. Most of us who have had influenza vaccines are familiar with the discomfort; a sore arm for one to two days, a "fluey" feeling of fatigue, achiness and headaches.
Do vaccines cause fever? It depends on age group and the vaccine. For the influenza vaccine, fever can occur in 12 per cent of children aged one to five, in 5 per cent of those six to 15 years old while in adults, no difference was observed compared with placebo, or dummy.
Very rarely, more serious events with long-term consequences, even death, can occur after vaccinations. This is known and accepted in medical and public health practice because the alternative is the disability and death caused by the actual infectious disease itself in much larger numbers and scale.
The problem for vaccine programmes is that their very success breeds complacency, and a loss of urgency for the vaccine when the disease is no longer seen.
Among serious adverse events from vaccines, yellow fever vaccination can cause liver or brain inflammation for three out of a million persons vaccinated. The people who get the yellow fever vaccine nowadays are travellers to South America and sub-Saharan Africa, and populations in those endemic countries.
Yellow fever sounds like an exotic disease, and we may hesitate to vaccinate travellers at higher risk for vaccine complications. But what is rarely appreciated is that yellow fever used to be far more widespread and devastating; the last yellow fever outbreak in the US occurred in 1905 in New Orleans, and Philadelphia lost 10 per cent of its entire population to yellow fever in the 1793 outbreak.
Yellow fever is spread by Aedes aegypti mosquitoes, familiar to us as the vector for dengue fever. However, unlike dengue which has a fatality rate of 1 in 1,000, yellow fever still carries a fatality rate of 20 per cent to 60 per cent among those severely ill.
So, the safety considerations for vaccination must take into account the other side of the equation: What happens without vaccination, not just for the individual, but also for entire cities and countries?
Polio, which caused epidemics leaving children and adults permanently paralysed, was stopped only by vaccination. The Sabin oral polio vaccine contains a live, weakened virus, which rarely causes vaccine-associated paralytic polio, at four in a million. Vaccine-associated polio happens to 400-500 persons per year worldwide, but when compared with the 350,000 polio cases in 1988 at the start of polio eradication efforts, the risk-benefit clearly favours vaccination.
If a serious event occurs after someone gets vaccinated, another challenge is to determine whether the event is caused by the vaccination, or whether it is a coincidental occurrence.
We have had influenza vaccines for over seven decades, giving over 150 million doses per year.
Yet when media reports surfaced of deaths following flu vaccination in South Korea, vaccination was paused until autopsies on 46 of the cases provided evidence that the deaths, mostly among people in their 70s and 80s, were likely to have been caused by existing medical conditions, and not the vaccine.
Events are top-line numbers, numerators. We need denominators to understand the true risk. The 50-90 deaths occurred on a denominator of 19 million Koreans vaccinated, so we must know the baseline rate of deaths to know if there are grounds for concern.