The vast majority of current COVID-19 cases are seen among unvaccinated people although many vaccinated with no record of travel history are infected with the Delta variant as well as the most recent Omicron variant. Many studies revealed that the Omicron spreads 70 times faster than the Delta variant and the original strain of COVID-19. However, the severity of the infection seems much lower and most of the Omicron cases have a mild infection and a low number of hospital admissions among infected.
Even if breakthroughs occur in vaccinated persons, it has been found that in most cases events are less severe than those in unvaccinated persons. However, studies consistently show a decline in vaccine effectiveness against SARS-CoV2 infection with the passage of time, and more significant decline found in older adults and people with underlying conditions. The debate on COVID-19 booster shots has existed ever since inoculations first began, with the scientific community trying their best to figure out how long the protection will last. Vaccine effectiveness against severe COVID-19 was found to have decreased by eight per cent over a period of six months in all age groups. Its efficacy against severe disease decreased by 10 per cent and against symptomatic disease by 32 per cent among adults over 50 years in the period of six months (WHO, 2021).
Safe for people All available COVID-19 vaccines are primarily disease-modifying and are primarily aimed at reducing the severity of infection, hospitalisation and death. In fact, they do not prevent infection. The coronavirus pandemic for more than two years shows that the herd immunity is most unlikely as chain of transmission continue even in countries with wide vaccination coverage. Boosters are being recommended by health authorities of many countries as emerging data shows that the protection against mild and moderate COVID-19 with vaccines decline over time. A booster is an additional dose of vaccine that can help prolong protective immunity in people who responded fully at first, but protection is declining after some time. It is intended to increase immunity against the viral antigen back to protective levels after memory against that antigen has declined over time.
The Centre for Disease Control (CDC) recommends that it is safe for people to get a booster shot different from the vaccines originally received (CDC, 2022). However, the recommendation is for Pfizer- BioNTech, Moderna and Johnson & Johnson’s Janssen vaccines. Currently, there is no study showing effectiveness of mix and match among Astra Zeneca Covishield and Vero Cell booster dose. Recently, Canadian Health Ministry (2022) recommended individuals who received AstraZeneca/Covishield COVID-19 vaccine for their first and second dose to receive an mRNA vaccine (viz. Pfizer-BioNTech or Moderna) for their third or booster dose.
It has been proved wrong that the COVID-19 pandemic would be a short lived. The vaccination drive will be continued for years to come until the virus is eradicated. The current COVID-19 vaccinations schedules are only priming are expected to wane over time. The protective levels of antibodies are said to be present for about six months to one year. Therefore, the recommended interval between priming and boosting is six months to one year. Vaccine effectiveness data for a booster dose has demonstrated an improvement in protection against infection, severe disease and death.
The World Health Organisation has reported that more than 125 countries have already issued recommendations on booster or additional dose. A large majority of them mainly are high-income or upper middle-income countries that have already started administering booster doses to target populations such as health workers, immuno-compromised people and older adults. Israel became the first country when it began offering a third dose of the Pfizer vaccine to severely immuno-compromised adults from July last year and extended eligibility to all citizens older than 12 years in August when a wave of infections driven by the Delta variant surged. Israeli studies have shown that a third shot offers significantly greater protection from severe illness and hospitalisation compared to just two doses. However, there is a difference between third dose and a booster dose. Third dose is primarily given to immune-compromised individuals after 2-5 months as they are not able to develop immunity to fight off infection and booster dose is given to all eligible people five months after the second dose.
Prioritisation Manufacturers worldwide are currently producing an estimated 1.5 billion doses of COVID-19 vaccine every month. So, in principle, it should be possible to offer boosters without hampering the supply of first and second inoculations in places with low immunisation rates. In many countries, everyone older than 12 years is now eligible for a booster, but not everyone is eligible immediately. In case of a person who has recently had COVID-19 and is eligible for a booster, it is recommended that to get booster shot after symptoms have resolved and the recommended time has elapsed since the primary series of vaccines.
The Government of Nepal has begun administering booster shots against COVID-19 to frontline workers from 17 January in the first phase and planning to inoculate booster to older adults above 60 years of age from January 29. In the first phase health, workers, security personnel, sanitation workers, journalists, ambulance drivers, and local government officials are expected to get booster shots.
It is important to keep in mind that vaccination may not always prevent from getting COVID-19, wearing a mask does. The immunity generated by vaccines helps to keep the infection from progressing to a severe case. The COVID-19 immunisation efforts must remain focused on decreasing death and severe disease, and overburdening our healthcare system. Besides vaccination campaign and an additional booster dose, public health and social preventive measures should remain an essential component of prevention strategy against this pandemic.
(Prof. Lohani is the clinical director at the Nepal Drug and Poison Information Center. email@example.com)