It’s Never Too Late: Post-exposure Vaccination in Outbreaks of Disease


In the past few months, San Diego has seen a spike in the number of hepatitis A cases; the San Diego County Board of Supervisors puts the latest count at 516 cases, including 357 hospitalizations and 19 deaths. In September, the board issued a public health emergency, along with a three-part response strategy to immunize, sanitize, and educate local residents to keep them safe and healthy. And, in late October, the board reported that nearly 84,000 vaccinations against hepatitis A had been administered in San Diego in response to the outbreak.

Vaccines, in fulfilling their original purpose, are preventative health tools meant to impede the potential for outbreaks of disease. Yet, outbreaks do occasionally occur and expose a large number of uninfected individuals who may not be immunized against diseases that are normally vaccine-preventable.

As indicated by San Diego’s response, vaccinating those who have already been exposed to a disease and may be at risk for infection is one of the best ways to curb an outbreak. In its guidelines and recommendations for several diseases, including hepatitis A, the Centers for Disease Control and Prevention (CDC) recommends what is called “post-exposure prophylaxis” for those who may have been exposed to the disease. The agency advises that individuals who have not been vaccinated previously should be given a single dose of the hepatitis A vaccine, or in some cases, its alternative immune globulin (IG), as quickly as possible.

Research originally published in the New England Journal of Medicine confirms that post-exposure prophylaxis is effective in curbing outbreaks and preventing infection in previously unvaccinated individuals. In the study, subjects who had not been vaccinated against hepatitis A, but had recent exposure to the disease, were given either IG or the hepatitis A vaccine, per the CDC’s guidelines. In both sets of subjects, the vaccine after exposure was more than 96% effective in preventing infection.

During San Diego’s hepatitis A outbreak, the county’s Director of Epidemiology and Immunization Services Branch followed the CDC advice and urged those who were potentially exposed to the disease to be vaccinated within two weeks—a recommendation taken directly from the CDC’s literature. To help facilitate vaccinations in such a short window, more than 250 vaccination events and 100 street teams had been utilized to ensure that San Diego residents were educated and protected, according to the board’s September report.

The effectiveness of the immunization in San Diego remains to be seen, but with more than 84,000 people immunized, the impact of this outbreak is expected to decrease soon. San Diego’s quick response to its rising case of hepatitis A provides an example and reminder to healthcare providers about how to approach post-exposure prophylaxis in communities where an outbreak occurs. It takes a village of providers educating patients and reminding that, even in the case of outbreaks, it’s never too late to be vaccinated.